1. Field of Application
The present invention relates to a process for high-efficiency catalytic conversion of carbon monoxide (CO) to carbon dioxide (CO2) of the type comprising the steps of:
feeding at predetermined speed a gaseous flow comprising carbon monoxide to a reaction space;
reacting the carbon monoxide in this space to obtain a gaseous flow comprising carbon dioxide.
In the description given below and in the following claims, the term: xe2x80x9creaction spacexe2x80x9d, is understood generally to mean a space comprising catalyst-containing means in which takes place the conversion reaction of carbon monoxide to carbon dioxide in accordance with the following formula.
CO+H2O(steam)⇄CO2+H2
Carbon monoxide conversion reaction is very important to industry because it permits obtaining one of the basic reagents for many synthesis reactions (for example ammonia synthesis), i.e. hydrogen (H2).
The present invention also relates respectively to a reactor and an equipment for implementation of the above process, so as to a modernization method respectively for a reactor and an apparatus for catalytic carbon monoxide conversion.
As known, in the field of catalytic carbon monoxide conversion the need is ever more strongly felt to provide easily implemented conversion processes, allowing achievement of ever higher production capacities at low operating and investment costs and low energy consumption.
2. Prior Art
To meet this requirement there have been proposed in the industry carbon monoxide conversion processes in which gaseous reagents were made to flow with substantially axial, radial or axial-radial motion across a reaction space comprising at least one catalytic bed.
A process of this type is described for example in EP-A-0 372 453.
Although advantageous in some ways, the processes according to the prior art all display a serious drawback linked to the presence of waterxe2x80x94e.g. in the form of dropsxe2x80x94entrained in the gaseous flow comprising carbon monoxide.
Indeed, water introduced together with the carbon monoxide into the reaction space irreversibly damages the surface layer of the catalyst contained therein and makes it extremely compact or packed.
This is due in particular to the localized thermal shock caused by the immediate evaporation of the water in contact with the high temperature catalyst, and in part to the mechanical impact of the water striking the catalyst.
The primary consequence of this packing of the surface layer of the catalyst is a significant pressure drop of the gaseous flow crossing the catalytic mass and a decrease in the activity of the catalyst, with associated decrease in conversion yield (and hence of productive capacity) and high energy consumption.
This important drawback of the carbon monoxide conversion processes according to the prior art has now been known for more than two decades, and the only solution proposed until now consists of manual elimination by a worker of the packed catalyst layer and its replacement with new catalyst.
In addition, formation of the packed catalyst layer can be so frequent and penalizing for the general behaviour of the process as to require the above mentioned treatment at very short time intervals generally less than a year (3 to 9 months).
As may be readily imagined, the present solution to the above mentioned drawback cannot be considered satisfactory for industry requirements because it involves stopping the plant assigned to implementation of the conversion process, and consequently stopping of production, high maintenance and operating costs and high energy consumption.
The problem underlying the present invention is to provide a carbon monoxide conversion process which would permit obtaining high production capacities and whose implementation would not involve high operating and investment costs nor high maintenance costs and energy consumption.
In particular, the problem underlying the present invention is to make available a carbon monoxide conversion process in which surface packing of the catalyst does not occur as it does in the processes according to the prior art.
The above mentioned problem is solved according to the present invention by a carbon monoxide conversion process of the above mentioned type, which is characterized in that it comprises the preliminary step of:
accelerating the gaseous flow comprising carbon monoxide upstream of the reaction space.
Advantageously, thanks to the step of accelerating the gaseous flow comprising carbon monoxide to be inlet to the reaction space, it is possible to obtain splitting of the water entrained therein in small diameter drops, e.g. between 100 xcexcm and 600 xcexcm, so as to promote at least partial evaporation of the latter in the feed gaseous flow which is generally not saturated with steam.
In addition, it was surprisingly found that following the acceleration step, the water drops resulting from the splitting all tend to concentratexe2x80x94for fluid mechanics reasonsxe2x80x94towards the centre of the feed gaseous flow so as to strike only a small circumscribed portion of the catalytic mass contained in the reaction space, while drastically limiting pressure drops due to catalyst packing.
Lastly, as a consequence of the above mentioned splitting of the water in small diameter drops, any damage to the catalyst by mechanical impact is substantially eliminated.
Thus, the process according to the present invention permits advantageously on the one hand at least partial elimination of the water entrained in the feed gaseous flow, and on the other hand drastic reduction of the catalyst portion struck by this entrainment as well as its damaging effect.
Preferably, the above mentioned acceleration is such as to increase the speed of the gaseous flow comprising carbon monoxide by a factor between 1.5 and 5 times, so as to obtain effective and complete splitting of all the water entrained in the gaseous flow.
Advantageously, the gaseous flow comprising carbon monoxide passes through the reaction space with substantially radial or axial/radial motion.
In this manner, the presence of water traces in the feed gaseous flow does not cause particular packing problems and hence pressure drop, since the portion of the reaction space struck by this residual entrainment is quite secondary and marginal.
For implementation of the above mentioned process, the present invention makes available a reactor for high efficiency catalytic conversion of carbon monoxide to carbon dioxide of the type comprising:
a substantially cylindrical external""shell;
at least one catalytic bed supported inside the above mentioned shell;
an inlet nozzle in fluid communication with the above mentioned shell to feed to said at least one catalytic bed a gaseous flow comprising carbon monoxide;
characterized in that it further comprises:
means for accelerating the gaseous flow supported upstream of the at least one catalytic bed.
As an alternative, the present invention is advantageously implemented by an equipment for high-efficiency catalytic conversion of carbon monoxide to carbon dioxide of the type comprising:
a conversion reactor comprising a substantially cylindrical shell and at least one catalytic bed supported in this shell;
a duct for feeding to the reactor the gaseous flow comprising carbon monoxide;
and characterized in that it further comprises:
means for accelerating the gaseous flow supported in the duct.
In accordance with another aspect of the present invention, there is also made available a method for modernization of a reactor for catalytic conversion of carbon monoxide to carbon dioxide of the type comprising:
a substantially cylindrical external shell;
at least one catalytic bed supported in the above mentioned shell;
an inlet nozzle in fluid communication with the shell to feed to the at least one catalytic bed a gaseous flow comprising carbon monoxide;
and characterized in that it comprises the step of:
arranging upstream of said at least one catalytic bed means for accelerating the gaseous flow.
In accordance with still another aspect of the present invention, there is also made available a method for modernization of an equipment for catalytic conversion of carbon monoxide to carbon dioxide of the type comprising:
a conversion reactor comprising a substantially cylindrical external shell and at least one catalytic bed supported in this shell;
a duct for feeding to said reactor a gaseous flow comprising carbon monoxide;
and characterized in that it comprises the step of:
arranging in the duct means for accelerating the gaseous flow.
Thanks to the above mentioned modernization methods respectively for an existing reactor or equipment, it is possible to obtain a carbon monoxide conversion process simple to implement and capable of achieving high production capacity at low operating cost and energy consumption and in which there does not occur surface packing of the catalyst contained in said at least one catalytic bed.